Simplify the following expression: $r = \dfrac{4a - 4}{4} \div \dfrac{5a}{4}$
Solution: Dividing by an expression is the same as multiplying by its inverse. $r = \dfrac{4a - 4}{4} \times \dfrac{4}{5a}$ When multiplying fractions, we multiply the numerators and the denominators. $r = \dfrac{ (4a - 4) \times 4 } { 4 \times 5a}$ $r = \dfrac{16a - 16}{20a}$ Simplify: $r = \dfrac{4a - 4}{5a}$